Variable valve control apparatus for internal combustion engine and method thereof

ABSTRACT

A requested volume flow ratio calculated based on a requested torque, an amount of two times a spit-back gas amount at the valve overlap time calculated based on a requested residual gas rate, and a spit-back gas amount of the time when an intake valve is closed are added together, to set a requested valve passing gas amount of the intake valve, thereby determining a target operating characteristic of the intake valve based on the requested valve passing gas amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/318,603, filed Dec.28, 2005, which is a divisional of U.S. Ser. No. 10/716,532, filed Nov.20, 2003, both of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a variable valve control apparatus anda variable valve control method for an internal combustion engine, andin particular to a technology for controlling an amount of workingmedium by variably controlling an operating characteristic of an intakevalve.

Heretofore, there has been known an apparatus in which a target torqueis set based on an accelerator opening and an engine rotation speed, andan operating characteristic of an intake valve is varied so that atarget intake air amount equivalent to the target torque can be obtained(refer to Japanese Unexamined Patent Publication No. 6-272580).

Further, there has also been known a variable valve event and liftmechanism that successively varies valve lifts of engine valves togetherwith operating angles of the engine valves (refer to Japanese UnexaminedPatent Publication No. 2001-012262).

Here, since there is a constant correlation between an opening area ofthe intake valve and a total amount of working medium in a cylinder, itis possible to estimate the total amount of working medium in thecylinder based on the opening area of the intake valve.

Note, the total amount of working medium in the cylinder is the sum of afresh air amount and a residual gas amount in the cylinder.

Further, the residual gas amount in the cylinder includes a spit-backgas amount to an intake side at the valve overlap time, a spit-back gasamount to the intake side at the intake valve closing time, and furthera residual gas amount which has not been discharged via an exhaust valveto remain in the cylinder.

In a region where the opening area of the intake valve is large, a gastemperature in the cylinder rises with an increase of residual gas, andvolume efficiency is lowered with the rise of gas temperature.

Accordingly, in the region where the opening area of the intake valve islarge, the total amount of working medium in the cylinder is changed todecrease relative to an increase of opening area.

Therefore, in the region where the opening area of the intake valve islarge, two opening areas exist corresponding to the total amount ofinner-cylinder working medium.

Here, if it is regarded that the total amount of inner-cylinder workingmedium is not changed relative to the increase of opening area, it ispossible to determine the number of opening areas corresponding to thetotal amount of inner-cylinder working medium to 1.

However, there is caused a problem of the occurrence of control error,if it is regarded that the total amount of inner-cylinder working mediumis not changed relative to the increase of opening area.

Further, a correlation between the opening area of the intake valve andan intake valve passing gas amount exists for each effective cylindercapacity that is changed depending on closing timing of the intakevalve.

Accordingly, in a system which controls an intake air amount using avariable valve mechanism that successively varies a valve lift and avalve operating angle, it is required to prepare a table indicating thecorrelation between the opening area ad the valve passing gas amount foreach effective cylinder capacity (closing timing of the intake valve).

However, if the table indicating the opening area and the valve passinggas amount is prepared for each effective cylinder capacity, largestorage capacity is required and also a large number of processes isrequired for matching each table.

SUMMARY

It is therefore an object of the present invention to enable a highaccurate control of a gas amount passing through an intake valve, basedon a correlation between an opening area of the intake valve and thevalve passing gas amount.

A further object of the present invention is to enable the control ofthe valve passing gas amount without the necessity of a large storagecapacity and also with a small number of matching processes.

In order to accomplish the above-mentioned objects, the presentinvention is constituted so that a fresh air amount flown into acylinder of an engine and a gas amount spit back to an intake side fromthe inside of the cylinder when the intake valve is opened arecalculated, and a gas amount passing through the intake valve iscalculated based on the fresh air amount and an amount of predeterminedtimes the spit-back gas amount of the time when the intake valve isopened, to control a variable valve mechanism based on the intake valvepassing gas amount.

Moreover, according to the present invention, a correlation between avalue equivalent to an opening area of the intake valve and the valvepassing gas amount is stored previously, the value equivalent to theopening area of the intake valve is converted into the valve passing gasamount by referring to the correlation, the value equivalent to theopening area is corrected based on a ratio between the valve passing gasamount obtained by the conversion and a requested valve passing gasamount, and requested effective cylinder capacity by which the requestedvalve passing gas amount can be obtained at the value equivalent to theopening area, is calculated based on the valve passing gas amountobtained by referring to the correlation based on the corrected valueequivalent to the opening area and the requested valve passing gasamount, to control the variable valve mechanism according to therequested effective cylinder capacity.

The other objects and features of the invention will become understoodfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a system structure of an internal combustionengine in an embodiment.

FIG. 2 is a cross section view showing a variable valve event and liftmechanism (A-A cross section of FIG. 3).

FIG. 3 is a side elevation view of the variable valve event and liftmechanism.

FIG. 4 is a top plan view of the variable valve event and liftmechanism.

FIG. 5 is a perspective view showing an eccentric cam for use in thevariable valve event and lift mechanism.

FIGS. 6(A) and 6(B) are cross sectional views showing an operation ofthe variable valve event and lift mechanism at a low lift condition (B-Bcross section view of FIG. 3).

FIGS. 7(A) and 7(B) are cross sectional views showing an operation ofthe variable valve event and lift mechanism at a high lift condition(B-B cross section view of FIG. 3).

FIG. 8 is a valve lift characteristic diagram corresponding to a baseend face and a cam surface of a swing cam in the variable valve eventand lift mechanism.

FIG. 9 is a characteristic diagram showing valve timing and a valve liftof the variable valve event and lift mechanism.

FIG. 10 is a perspective view showing a rotational driving mechanism ofa control shaft in the variable valve event and lift mechanism.

FIG. 11 is a longitudinal cross section view of a variable valve timingmechanism in the embodiment.

FIG. 12 is a block diagram showing the calculation of requested closingtiming of an intake valve in the embodiment.

FIG. 13 is a block diagram showing the calculation of a requested valvepassing gas amount in the embodiment.

FIG. 14 is a block diagram showing the calculation of a spit-back gasamount in the closing timing of the intake valve in the embodiment.

FIG. 15 is a graph showing, at each closing timing, a correlationbetween an opening area of the intake valve and the valve passing gasamount in the embodiment.

FIG. 16 is a block diagram showing the calculation of requested openingtiming of the intake valve in the embodiment.

FIG. 17 is a block diagram showing the calculation of a target operatingcharacteristic of the intake valve in the embodiment.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a system structure of an internal combustionengine for vehicle comprising a variable valve mechanism according tothe present invention.

In FIG. 1, in an intake passage 102 of an internal combustion engine101, an electronically controlled throttle 104 is disposed for driving athrottle valve 103 b to open and close by a throttle motor 103 a.

Air is sucked into a combustion chamber 106 via electronicallycontrolled throttle 104 and an intake valve 105.

A combusted exhaust gas is discharged from combustion chamber 106 via anexhaust valve 107.

Then, the combusted exhaust gas is purified by an exhaust purificationcatalyst 108 and thereafter, emitted into the atmosphere via a muffler109.

Exhaust valve 107 is driven by a cam 111 axially supported by an exhaustside camshaft 110, to open and close at fixed valve lift amount, valveoperating angle and valve opening/closing timing.

A valve lift and a valve operating angle of intake valve 105 are variedsuccessively by a variable valve event and lift mechanism (to bereferred to as VEL hereunder) 112.

On an end portion of an intake side camshaft 113, there is disposed avariable valve timing mechanism (to be referred to as VTC hereunder) 114that varies successively a center phase of the operating angle of intakevalve 105 by changing a rotation phase of intake side camshaft 113relative to a crankshaft.

A control unit 115 incorporating therein a microcomputer, receivesvarious detection signals from an accelerator opening sensor APS 116, anair flow meter 117 detecting an intake air amount (mass flow amount) Qa,a crank angle sensor 118 taking out a rotation signal Ne from thecrankshaft, a cam sensor 119 detecting a rotation position of intakeside camshaft 113, a throttle sensor 120 detecting an opening TVO ofthrottle valve 103 b, and the like.

Then, control unit 115 adjusts an amount of working medium of engine 101by the control of an operating characteristic of intake valve 105 by VEL112 and VTC 114.

Further, control unit 115 controls an opening of throttle valve 103 b sothat a fixed negative pressure (for example, −50 mmHg) is generated forcanister purging and blow-by gas processing.

Here, the structure of VEL 112 will be described.

VEL 112, as shown in FIG. 2 to FIG. 4, includes a pair of intake valves105, 105, a hollow camshaft 13 rotatably supported by a cam bearing 14of a cylinder head 11, two eccentric cams 15, 15 being rotation cams,axially supported by camshaft 13, a control shaft 16 rotatably supportedby cam bearing 14 and arranged at an upper position of camshaft 13, apair of rocker arms 18,18 swingingly supported by control shaft 16through a control cam 17, and a pair of swing cams 20, 20 disposedindependently from each other to upper end portions of intake valves105, 105 through valve lifters 19, 19, respectively.

Eccentric cams 15, 15 are connected with rocker arms 18, 18 by link arms25, 25, respectively, and rocker arms 18,18 are connected with swingcams 20, 20 by link members 26, 26.

Each eccentric cam 15, as shown in FIG. 5, is formed in a substantiallyring shape and includes a cam body 15 a of small diameter, a flangeportion 15 b integrally formed on an outer surface of cam body 15 a. Acamshaft insertion hole 15 c is formed through the interior of eccentriccam 15 in an axial direction, and also a center axis X of cam body 15 ais biased from a center axis Y of camshaft 13 by a predetermined amount.

Eccentric cams 15, 15 are pressed and fixed to camshaft 13 via camshaftinsertion holes 15 c at outsides of valve lifters 19, 19, respectively,so as not to interfere with valve lifters 19, 19. Also, outer peripheralsurfaces of cam body 15 a are formed in the same cam profile.

Each rocker arm 18, as shown in FIG. 4, is bent and formed in asubstantially crank shape, and a central base portion 18 a thereof isrotatably supported by control cam 17.

A pin hole 18 d is formed through one end portion 18 b which is formedto protrude from an outer end portion of base portion 18 a. A pin 21 tobe connected with a tip portion of link arm 25 is pressed into pin hole18 d. A pin hole 18 e is formed through the other end portion 18 c whichis formed to protrude from an inner end portion of base portion 18 a. Apin 28 to be connected with one end portion 26 a (to be described later)of each link member 26 is pressed into pin hole 18 e.

Control cam 17 is formed in a cylindrical shape and fixed to a peripheryof control shaft 16. As shown in FIG. 2, a center axis P1 position ofcontrol cam 17 is biased from a center axis P2 position of control shaft16 by α, thereby creating spacing 17 a.

Swing cam 20 is formed in a substantially lateral U-shape as shown inFIG. 2, FIG. 6 and FIG. 7, and a supporting hole 22 a is formed througha substantially ring-shaped base end portion 22. Camshaft 13 is insertedinto supporting hole 22 a to be rotatably supported. Also, a pin hole 23a is formed through an end portion 23 positioned at the other endportion 18 c of rocker arm 18.

A base circular surface 24 a of base end portion 22 side and a camsurface 24 b extending in an arc shape from base circular surface 24 ato an edge of end portion 23, are formed on a bottom surface of swingcam 20. Base circular surface 24 a and cam surface 24 b are in contactwith a predetermined position of an upper surface of each valve lifter19 corresponding to a swing position of swing cam 20.

Namely, according to a valve lift characteristic shown in FIG. 8, asshown in FIG. 2, a predetermined angle range θ1 of base circular surface24 a is a base circle interval and a range of from base circle intervalθ1 of cam surface 24 b to a predetermined angle range θ2 is a so-calledramp interval, and a range of from ramp interval θ2 of cam surface 24 bto a predetermined angle range θ3 is a lift interval.

Link arm 25 includes a ring-shaped base portion 25 a and a protrusionend 25 b protrudingly formed on a predetermined position of an outersurface of base portion 25 a. A fitting hole 25 c to be rotatably fittedwith the outer surface of cam body 15 a of eccentric cam 15 is formed ona central position of base portion 25 a. Also, a pin hole 25 d intowhich pin 21 is rotatably inserted is formed through protrusion end 25b.

Link arm 25 and eccentric cam 15 consist a swing-drive member.

Link member 26 is formed in a linear shape of predetermined length andpin insertion holes 26 c, 26 d are formed through both circular endportions 26 a, 26 b. End portions of pins 28, 29 pressed into pin hole18 d of the other end portion 18 c of rocker arm 18 and pin hole 23 a ofend portion 23 of swing cam 20, respectively, are rotatably insertedinto pin insertion holes 26 c, 26 d.

Snap rings 30, 31, 32 restricting axial transfer of link arm 25 and linkmember 26 are disposed on respective end portions of pins 21, 28, 29.

Control shaft 16 is driven to rotate within a predetermined angle rangeby an actuator 201, such as a DC servo motor, disposed on one endportion thereof, as shown in FIG. 10. By varying an angle of controlshaft 16 by actuator 201, the valve lift amount and valve operatingangle of each of intake valves 105, 105 are successively varied (referto FIG. 9).

Namely, in FIG. 10, the rotation of actuator (for example, DC servomotor) 201 is transmitted to a threaded shaft 203 via a transmissionmember 202, to change the axial position of a nut 204 through whichshaft 203 is inserted.

Control shaft 16 is rotated by a pair of stays 205 a, 205 b, eachmounted on the tip end of control shaft 16 and one end thereof fixed tonut 204.

In this embodiment, as shown in the figure, the valve lift amount isdecreased as the position of nut 204 approaches transmission member 202,while the valve lift amount is increased as the position of nut 204 getsaway from transmission member 202.

Further, a potentiometer type angle sensor 206 detecting the angle ofcontrol shaft 16 is disposed on the tip end of control shaft 16. Controlunit 115 feedback controls actuator 201 so that an actual angle detectedby angle sensor 206 coincides with a target angle.

Next, the structure of VTC 113 will be described based on FIG. 11.

Note, VTC 114 is not limited to the one in FIG. 11, and may be of theconstitution to successively vary a rotation phase of a camshaftrelative to a crankshaft.

VTC 114 in this embodiment is a vane type variable valve timingmechanism, and comprises: a cam sprocket 51 (timing sprocket) which isrotatably driven by a crankshaft 120 via a timing chain; a rotationmember 53 secured to an end portion of intake side camshaft 113 androtatably housed inside cam sprocket 51; a hydraulic circuit 54 thatrelatively rotates rotation member 53 with respect to cam sprocket 51;and a lock mechanism 60 that selectively locks a relative rotationposition between cam sprocket 51 and rotation member 53 at predeterminedpositions.

Cam sprocket 51 comprises: a rotation portion (not shown in the figure)having on an outer periphery thereof, teeth for engaging with timingchain (or timing belt); a housing 56 located forward of the rotationportion, for rotatably housing rotation member 53; and a front cover anda rear cover (not shown in the figure) for closing the front and rearopenings of housing 56.

Housing 56 presents a cylindrical shape formed with both front and rearends open and with four partition portions 63 protrudingly provided atpositions on the inner peripheral face at 90° in the circumferentialdirection, four partition portions 63 presenting a trapezoidal shape intransverse section and being respectively provided along the axialdirection of housing 56.

Rotation member 53 is secured to the front end portion of intake sidecamshaft 113 and comprises an annular base portion 77 having four vanes78 a, 78 b, 78 c, and 78 d provided on an outer peripheral face of baseportion 77 at 90° in the circumferential direction.

First through fourth vanes 78 a to 78 d present respectivecross-sections of approximate trapezoidal shapes. The vanes are disposedin recess portions between each partition portion 63 so as to formspaces in the recess portions to the front and rear in the rotationdirection. Advance angle side hydraulic chambers 82 and retarded angleside hydraulic chambers 83 are thus formed.

Lock mechanism 60 has a construction such that a lock pin 84 is insertedinto an engagement hole (not shown in the figure) at a rotation position(in the reference operating condition) on the maximum retarded angleside of rotation member 53.

Hydraulic circuit 54 has a dual system oil pressure passage, namely afirst oil pressure passage 91 for supplying and discharging oil pressurewith respect to advance angle side hydraulic chambers 82, and a secondoil pressure passage 92 for supplying and discharging oil pressure withrespect to retarded angle side hydraulic chambers 83. To these two oilpressure passages 91 and 92 are connected a supply passage 93 and drainpassages 94 a and 94 b, respectively, via an electromagnetic switchingvalve 95 for switching the passages.

An engine driven oil pump 97 for pumping oil in an oil pan 96 isprovided in supply passage 93, and the downstream ends of drain passages94 a and 94 b are communicated with oil pan 96.

First oil pressure passage 91 is formed substantially radially in a base77 of rotation member 53, and connected to four branching paths 91 dcommunicating with each advance angle side hydraulic chamber 82. Secondoil pressure passage 92 is connected to four oil galleries 92 d openingto each retarded angle side hydraulic chamber 83.

With electromagnetic switching valve 95, an internal spool valve isarranged so as to control relatively the switching between respectiveoil pressure passages 91 and 92, and supply passage 93 and drainpassages 94 a and 94 b.

Control unit 115 controls the power supply quantity for anelectromagnetic actuator 99 that drives electromagnetic switching valve95, based on a duty control signal superimposed with a dither signal.

For example, when a control signal of duty ratio 0% (OFF signal) isoutput to electromagnetic actuator 99, the hydraulic fluid pumped fromoil pump 97 is supplied to retarded angle side hydraulic chambers 83 viasecond oil pressure passage 92, and the hydraulic fluid in advance angleside hydraulic chambers 82 is discharged into oil pan 96 from firstdrain passage 94 a via first oil pressure passage 91.

Consequently, an inner pressure of retarded angle side hydraulicchambers 83 becomes a high pressure while an inner pressure of advanceangle side hydraulic chambers 82 becomes a low pressure, and rotationmember 53 is rotated to the most retarded angle side by means of vanes78 a to 78 d. The result of this is that a valve opening period (openingtiming and closing timing) is delayed.

On the other hand, when a control signal of duty ratio 100% (ON signal)is output to electromagnetic actuator 99, the hydraulic fluid issupplied to inside of advance angle side hydraulic chambers 82 via firstoil pressure passage 91, and the hydraulic fluid in retarded angle sidehydraulic chambers 83 is discharged to oil pan 96 via second oilpressure passage 92, and second drain passage 94 b, so that retardedangle side hydraulic chambers 83 become a low pressure.

Therefore, rotation member 53 is rotated to the full to the advanceangle side by means of vanes 78 a to 78 d. Due to this, the openingperiod (opening timing and closing timing) of intake valve 105 isadvanced.

Note, variable valve timing mechanism 114 is not limited to the abovevane type mechanism, and may be of the constitution as disclosed inJapanese Unexamined Patent Publication Nos. 2001-041013 and 2001-164951in which a rotation phase of a camshaft relative to a crankshaft ischanged by friction braking of an electromagnetic clutch(electromagnetic brake), or of the constitution as disclosed in JapaneseUnexamined Patent Publication No. 9-195840 in which a helical gear isoperated by a hydraulic pressure.

Next, there will be described controls of VEL 112 and VTC 114, bycontrol unit 115, referring to block diagrams.

The block diagram of FIG. 12 shows the calculation of requested closingtiming of intake valve 105.

In FIG. 12, a requested engine torque calculated based on theaccelerator opening and the like is converted into a requested volumeflow ratio TQHOST (requested fresh air amount) in b101.

In b102, a requested valve passing gas amount in intake valve 105 iscalculated based on the requested volume flow ratio TQHOST, an upstreampressure of intake valve 105 and a requested residual gas rate.

The calculation of requested valve passing gas amount in b102 isexecuted as shown in the block diagram of FIG. 13.

In FIG. 13, in b501, a target residual gas rate is calculated based onthe requested volume flow ratio TQHOST and the engine rotation speed Ne.

In b502, target residual gas mass is calculated based on the targetresidual gas rate and the requested volume flow ratio TQHOST.

In b503, the target residual gas mass is divided into a residual gasamount that has not been discharged at the closing time of exhaust valve107, to remain in the cylinder just as it is, and a spit-back gas amountspit-back to an intake pipe side at the valve overlap time (at theopening time of intake valve).

In b504, the spit-back gas amount at the valve overlap time is doubled.

In b505, the amount of two times the spit-back gas amount at the valveoverlap time and the spit-back gas amount at the closing time of intakevalve 105 to be calculated in b506 are added together.

It is supposed that the gas spit-back to the intake pipe side at thevalve overlap time is again flown into the cylinder. As a result, thegas passes through intake valve 105 twice and therefore, is doubled.

However, the spit-back gas is not necessarily doubled, and whatmultiplication is performed on the spit-back gas should be appropriatelyset according to the actual behavior of spit-back gas at the valveoverlap time.

In b507, the sum of the doubled amount of the spit-back gas amount atthe valve overlap time to be calculated as mass and the spit-back gasamount at the closing time of intake valve 105, is converted into avolume flow ratio.

Then, in b508, the volume flow ratio obtained in b507 and the requestedvolume flow ratio TQHOST are added together, and a result of theaddition is finally output as the requested valve passing gas amount.

That is, the requested valve passing gas amount is calculated based on afresh air amount, the doubled amount of the spit-back gas amount at thevalve overlap time (the spit-back gas amount at the opening time ofintake valve) and the spit-back gas amount at the closing time of intakevalve.

The spit-back gas amount at the closing time of intake valve iscalculated as shown in the block diagram of FIG. 14.

In FIG. 14, in b601, an opening area AIVC of intake valve 105correlating to the spit-back gas amount is obtained based on targetclosing timing of intake valve 105 and a target angle TGVEL of controlshaft 16 in VEL 112.

In b602, the opening area AIVC obtained in b601 is converted into abasic spit-back gas amount WIVCO at the closing time of intake valve.

On the other hand, in b603, a correction value KPMPE based on an intakepressure Pm is calculated, and in b604, a correction value KHOSNE basedon the engine rotation speed Ne is calculated.

Then in b605, the correction value KPMPE is multiplied on the basicspit-back gas amount WIVCO, and in b606, a result of multiplication inb605 is further multiplied by the correction value KHOSNE. A result ofmultiplication in b606 is output as a final spit-back gas amount at theclosing time of intake valve.

The requested valve passing gas amount calculated in the above mannertends to be increased in all of the regions relative to an increase ofopening area of intake valve 105, as shown in FIG. 15.

Accordingly, based on the correlation between the valve passing gasamount and the opening area, a request of opening area for obtaining therequested valve passing gas amount is primarily determined.

Then, the opening area for obtaining the requested valve passing gasamount is obtained based on an actual correlation between the valvepassing gas amount and the opening area, thereby enabling of a highaccurate control of valve operating characteristic.

Here, the description shall be returned to the block diagram of FIG. 12to be continued.

In b103, an angle INPVEL of control shaft 16 in VEL 112 is set forcalculating the target opening timing and target closing timing ofintake valve.

The angle INPVEL is sequentially updated so as to calculate the targetopening timing and target closing timing for each valve lift amountwithin a control range.

The angle INPVEL is converted into an opening area TVELAA of intakevalve 105 in b104.

In b105, the opening area TVELAA is divided by the engine rotationnumber (rpm) at the time.

In b106, a result of division in b105 is further divided by a pistondisplacement VOL# of engine 101, so that the opening area TVELAA isconverted into a state amount AADNV.

The state amount AADNV is converted into a reference valve passing gasamount of intake valve 105 in b107.

A correlation between the state amount AADNV and the valve passing gasamount exists for each effective cylinder capacity. Here, a table isprepared for a correlation of the time when the effective cylindercapacity is 100%.

Note, when the closing timing of intake valve is made a bottom deadcenter, the effective cylinder capacity is 100%.

Then, the above conversion table is referred to, so that the stateamount AADNV is converted into the reference valve passing gas amount.

In b108, the reference valve passing gas amount is divided by therequested valve passing gas amount comprising the fresh air amount, thedoubled amount of the spit-back gas amount at the valve overlap time andthe spit-back gas amount at the closing timing of intake valve.

In b109, a calculation result in b108 is multiplied on the state amountAADNV.

That is, an output from b109 has the following value.

Output AADNV′ from b109=AADNV×(reference valve passing gasamount/requested valve passing gas amount)

In b111, by referring to the conversion table same as that referred toin b107, the valve passing gas amount corresponding to the state amountAADNV′ corrected in b109 is obtained.

In bill, the requested valve passing gas amount is divided by the valvepassing gas amount obtained in b110, to obtain a requested cylindercapacity ratio.

Requested cylinder capacity ratio=Requested valve passing gasamount/valve passing gas amount corresponding to AADNV′

In b112, the requested cylinder capacity ratio is converted into therequested closing timing of intake valve 105 according to the enginerotation speed Ne at the time.

The requested closing timing of intake valve 105 is set such that intakevalve 105 is closed before the bottom dead center as the requestedcylinder capacity ratio becomes smaller.

The correlation between the state amount AADNV and the valve passing gasamount exists for each effective cylinder capacity. As shown in FIG. 15,the characteristic lines of the state amount AADNV and the valve passinggas amount are in a relation similar to each other.

Here, the referring to the correlation of the time when the effectivecylinder capacity=100% based on the state amount AADNV′ corrected basedon the reference valve passing gas amount/requested valve passing gasamount equals to the referring to the correlation obtained by similarlyenlarging the correlation in the effective cylinder capacity by whichthe requested valve passing gas amount can be obtained based on thestate amount AADNV.

Then, the requested valve passing gas amount is divided by the valvepassing gas amount obtained by referring to the correlation of the timewhen the effective cylinder capacity=100% based on the state amountAADNV′, resulting in that the effective cylinder capacity for obtainingthe requested valve passing gas amount is obtained based on the angleINPVEL at the time.

If the constitution is such that the effective cylinder capacity forobtaining the requested valve passing gas amount is obtained based onthe angle INPVEL at the time, as described above, since it is onlynecessary to store the correlation between the state amount AADNV of thetime when the effective cylinder capacity=100% and the valve passing gasamount, it is possible to reduce the storage capacity and the matchingprocesses.

On the other hand, the requested opening timing of intake valve 105 isset as shown in the block diagram of FIG. 16.

In b201, the target residual gas rate is set based on the requestedvolume flow ratio TQHOST and the engine rotation speed Ne.

In b202, the target residual gas mass is calculated based on the targetresidual gas rate and the requested volume flow ratio TQHOST.

In b203, the target residual gas mass is divided into a portion toremain as it is in the cylinder at closing timing of exhaust valve 107and a portion to be spit back at the valve overlap time.

In b204, the requested opening timing of intake valve 105 is calculatedbased on the spit-back portion at the valve overlap time, the enginerotation speed Ne and the intake pressure.

The block diagram of FIG. 17 shows the calculation of a control targetangle TGVEL of control shaft 16 in VEL 112 based on the requestedclosing timing and requested opening timing of intake valve 105 and alsothe calculation of an advance control target by VTC 114.

In b301, a requested operating angle REQEVENT is calculated based on therequested closing timing and requested opening timing of intake valve105.

In b302, the angle INPVEL is converted into an operating angle CALEVENTof intake valve 105.

Then, in b303, the control target angle TGVEL is calculated based on theabove described REQEVENT and CALEVENT.

Specifically, a deviation between REQEVENT and CALEVENT is calculated tobe stored for each angle INPVEL, to select a combination of the angleINPVEL at which an absolute value of the deviation becomes smallest, therequested closing timing and the requested opening timing.

Then, the angle INPVEL at which the absolute value of the deviationbecomes smallest is set to the control target angle TGVEL, and therequested closing timing and the requested opening timing calculatedcorresponding to the angle INPVEL at which the absolute value of thedeviation becomes smallest are set as final target opening/closingtiming, to be output together with the control target angle TGVEL tob304.

In b304, an advance target of valve timing for achieving the targetopening/closing timing at the control target angle TGVEL, that is, acontrol target TGVTC of VTC 114, is set.

Then, VTC 114 is controlled based on the control target TGVTC, and thecenter phase of the operating angle of intake valve 105, which isdetermined based on the control target angle TGVEL, is controlled to beadvanced or retarded in accordance with the control target TGVTC.

Thus, intake valve 105 is driven at the opening area and theopening/closing timing, at which the requested valve passing gas amountand the requested residual gas rate can be obtained.

The entire contents of Japanese Patent Application Nos. 2002-350276 and2002-350277, filed Dec. 2, 2002, respectively, priorities of which areclaimed, are incorporated herein by reference.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims.

Furthermore, the foregoing description of the embodiments according tothe present invention are provided for illustration only, and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

1. A variable valve control method for an internal combustion engineprovided with a variable valve mechanism that varies an operatingcharacteristic of an intake valve, for controlling a gas amount passingthrough said intake valve by variably controlling said operatingcharacteristic, comprising the steps of: calculating an amount of freshair that flows into a cylinder based on a requested torque; calculatinga gas amount spit-back to an intake side from the inside of the cylinderwhen said intake valve is opened, based on a requested residual gasrate; calculating a requested gas amount passing through said intakevalve, based on an amount of predetermined times the spit-back gasamount of the time when said intake valve is opened and said fresh airamount; setting a target operating characteristic of said intake valvebased on said requested valve passing gas amount; and controlling saidvariable valve mechanism based on said target operating characteristic.2. A variable valve control method for an internal combustion engineaccording to claim 1, wherein there are provided, as said variable valvemechanism, a variable valve event and lift mechanism that successivelyvaries a valve lift of said intake valve together with an operatingangle of said intake valve, and a variable valve timing mechanism thatsuccessively varies a center phase of the operating angle of said intakevalve; and wherein said step of controlling said variable valvemechanism comprises the steps of: calculating requested closing timingof said intake valve, at which said requested valve passing gas amountcan be obtained, when an opening area of said intake valve is apredetermined value; calculating requested opening timing of said intakevalve based on said residual gas rate and said predetermined openingarea; setting, as a control target of said variable valve event and liftmechanism, a valve lift or an operating angle which satisfies, with saidpredetermined opening area, an operating angle obtained based on saidrequested closing timing and requested opening timing; and setting acontrol target of said variable valve timing mechanism so as to satisfysaid requested closing timing and requested opening timing.